This invention relates to an electric temperature setback device used to control a thermostat at pre-determined times and for pre-determined intervals.
Recent emphasis on saving energy and reducing expenditures for fuel has resulted in the development of many new devices for adjusting the temperature setting on a heating system thermostat. By regulating the setting of the thermostat, the heating system can be made to raise a building temperature to a pre-determined, relatively high level, during periods of occupancy and lower the temperature during other times. For example, a setback device on a thermostat in a residential dwelling can be set so as to lower the temperature substantially during the nighttime hours while the occupants are asleep. The thermostat can be programmed to raise the temperature to a more comfortable level shortly before they awake. If the dwelling is empty during the day while its occupants are at work or in school, as is often the case, the setback device can be set to again lower the temperature within the dwelling during the day and then raise the temperature to a more comfortable level in the late afternoon shortly before the occupants return. The dwelling is kept at this relatively warm temperature during the early evening hours and until the occupants again retire, completing the daily cycle. Depending on the sophistication of the unit, temperatures can be adjusted to differing levels and control for longer periods of time.
One way in which this setback ability has been accomplished is the substitution of a conventional thermostat with a much more expensive unit containing a built-in timer and means for setting the temperature which will be maintained by the thermostat during various intervals. Some of these units are operated by batteries, while other units require running 110 volt AC service to the thermostat outlet in addition to the usual low voltage service. These units are relatively expensive and require replacement of the existing thermostat. In addition, extra wiring is sometimes required.
Another type of device used to set back a thermostat involves the use of a local heat source which is connected to a timer. The heat source is placed in close proximity to the thermostat (usually below it) and permits a flow of air past the heat source into the sensing zone of the thermostat. By providing this local warmth, the thermostat itself need not be adjusted. Rather, the thermostat senses this local warmth and maintains the heating system in an "off" condition. Of course, the air temperature in the dwelling is thus permitted to drop to a level substantially below what the thermostat itself reads. Many of these units also have a built-in timer for controlling the intervals during which the heat source is providing warmth to the thermostat.
Other devices are also provided with adjustment means, such as rheostats, so that the warmth provided to the thermostat can be controlled, thereby varying the extent to which the temperature is permitted to drop. While these devices are generally less expensive than the combination thermostat-timer type and permit the continued use of an existing thermostat, many have numerous moving parts and are therefore still relatively expensive. Other devices, while more simple, use one or more incandescent light sources which provide, in addition to heat, a relatively high percentage of unnecessary and undesirable light.
So far as is known, no simple and inexpensive device has heretofore been devised which can be adapted for use with a conventional thermostat and which will efficiently provide sufficient heat to set back a thermostat, when desired, to a pre-determined level.